(Not Applicable)
(Not Applicable)
The present invention relates generally to valve seals, and more particularly to a combination face and plug seal particularly suited for use in a pressure balanced valve.
There is currently known in the prior art balanced valves which include pressure balanced shafts and plugs that are displaced during normal operation of the valve. A balanced shaft or plug typically includes holes or apertures through its length to ensure that pressure forces are balanced on either side of the shaft or plug. This balancing of pressure forces significantly reduces the force required to actuate the valve, and more particularly the movement of the plug between its open and closed positions. These particular types of valves include a xe2x80x9cbalance sealxe2x80x9d which extends about and is engageable to the plug to prevent upstream pressure from causing fluid to leak downstream of the plug. The balanced plugs are often located in a pipe or ducting system in order to control fluid flow by essentially blocking that flow to varying degrees. The plugs are themselves typically fabricated from sturdy blocks of metal and moved by rods into and out of the fluid flow. The balance seal normally acts against the side surface of the plug and, as indicated above, is placeable into sealed engagement with the plug to prevent upstream pressure from causing fluid to leak downstream of the plug.
In currently known balanced valves, the balance seal typically resides within a complementary channel or recess, and is often formed to include a portion which is deformed or deflected when exposed to pressure such that the deflected or deformed portion moves into sealed engagement with the valve plug. As such, the balance seal is often fabricated from a soft material to provide the requisite level of flexion/deformability. However, leakage problems arise when the valve including the balanced plug is used in certain applications. More particularly, in certain applications, a leakage path is defined between the balance seal and the walls of the complementary recess within the valve housing into which the balance seal is received, thus facilitating the undesirable leakage of upstream pressure downstream of the valve plug despite the sealed engagement of the deflected or deformed portion of the balance seal with the valve plug. This type of leakage problem often arises when the valve including the balance plug is used in cryogenic service applications wherein the temperature of the fluid flowing therethrough is about xe2x88x9250xc2x0 Fahrenheit or below, with these extremely low temperatures facilitating shrinkage in the material of the balance seal which compromises its ability to maintain sealed contact with the valve housing. As indicated above, the insufficiency of the sealed engagement between the balance seal and the valve housing facilitates the undesirable leakage of upstream pressure downstream of the valve plug.
Such leakage may also occur as a result of the insufficiency of the sealed engagement between the balance seal and the valve plug itself, which also may occur in valves used in cryogenic service applications due to the balance seal not being configured to provide a level of flexion/deformability which is capable of maintaining sealed engagement to the valve plug despite the loss of softness/resiliency attributable to the extremely low fluid temperature. The present invention is adapted to overcome the above-described deficiencies by providing a combination face and plug seal which is adapted to prevent the aforementioned leakage problems typically encountered with existing balance seals.
In accordance with a first embodiment of the present invention, there is provided a combination face and plug seal for use in a balanced pressure valve having a valve housing and a valve plug movable within the valve housing between an open position and a closed position. The seal comprises a main body portion having an engagement portion integrally connected thereto via an intermediate connection portion. The engagement portion includes a sealing surface which defines a central opening sized to accommodate the valve plug. A pair of primary springs extend along and at least partially between the main body and engagement portions in opposed relation to each other, with each of the primary springs defining a primary seal well. The seal of the first embodiment further comprises a pair of seal leg portions which are integrally connected to the main body portion in opposed relation to each other and each define an engagement surface. A pair of secondary springs extend along and at least partially between the main body portion and respective ones of the seal leg portions in opposed relation to each other, with the secondary springs each defining a secondary seal well. The main body, engagement and seal leg portions, as well as the primary and secondary springs, are each annular. The sealing surface defined by the engagement portion is preferably arcuately contoured (e.g., concave), with the engagement surface defined by each of the seal leg portions optionally including serrations formed therein.
The seal of the first embodiment is adapted to be retained within a complementary recess within the valve housing. The orientation of the valve plug in its closed position and/or the movement of the valve plug from its closed position toward its open position facilitates the forcing of the engagement portion into sealed engagement with the valve plug and the forcing of the seal leg portions into sealed engagement with the valve housing. In this regard, the engagement portion and primary springs are each deformable upon the application of pressure to the primary seal wells such that at least a portion of the sealing surface is forced into sealed engagement with the valve plug. Similarly, the seal leg portions and secondary springs are each deformable upon the application of pressure to the secondary seal wells such that at least a portion of the engagement surface of each of the seal leg portions is forced into sealed engagement with the valve housing. The main body, engagement and seal leg portions of the seal are each preferably fabricated from virgin polytetrafluorethylene, with the primary and secondary springs each preferably being fabricated from a resilient metallic material.
In accordance with a second embodiment of the present invention, there is provided a seal configured as essentially one-half the seal of the first embodiment. In this regard, the seal of the second embodiment includes only one seal leg portion, only one primary spring and only one secondary spring, with the primary and secondary springs being disposed on a common side of the remainder of the seal.